The present invention relates to a bonding material for bonding a polymeric veneering material or ceramic to the metal framework or understructure of a dental restoration or prosthesis.
In a metal based aesthetic dental restoration such as a dental crown and/or a bridge, a metal framework forms the understructure of the restoration, over which is applied a polymer based veneering material or a ceramic porcelain. The veneering material or ceramic is connected to the underlying metal framework to form the superstructure of the prosthesis or dental restoration. The metal framework can represent the metal overlay or metal underlay in a dental restoration or a metal coping in a crown or bridge.
To enhance the bond strength between the veneering material and the metal framework or coping it is conventional practice to first apply a bonder to the surface of the metal framework before coating the surface with the veneering material or porcelain. Commercially available bonders form a mechanical or chemical bond between the bonder and the metal framework. For polymer based veneering materials such as, for example, acrylics or resins which are applied as a coating over the metal framework the retention between the veneering material and the metal framework is relatively weak and the bond strength between the veneering material and the metal framework is poor.
The bonding material of the present invention forms a fused autogenous bond at the interface between the bonding material and the metal surface and forms an interlock of high mechanical retention to the veneering material resulting in a bond between the veneering material and metal framework or coping which is essentially unbreakable.
The dental bonding material of the present invention comprises a composition of precious metal particles consisting essentially of high fusing temperature metal particles of irregular geometry having a melting temperature above at least about 1200xc2x0 C. in a size range between 1 micron and 150 microns and low fusing temperature metal particles having a melting temperature below about 1080xc2x0 C. with or without a suitable carrier for coating or brushing the dental bonding material upon the surface of a metal coping. The dental bonding material may further include a flux of conventional composition preferably containing the element boron. The concentration of the flux should be in the range of between 0 and 5% by weight of the dental material.
The method of bonding a polymeric veneering material to a metal surface of a metal framework or coping in forming a dental restoration or prosthesis according to the present invention comprises forming a dental bonding material comprising a composition of precious metal particles consisting essentially of high fusing temperature metal particles having a melting temperature above at least about 1200xc2x0 C. in a size range between 1 micron and 150 microns and low fusing temperature metal particles having a melting temperature below about 1080xc2x0 C., coating the metal surface with bonding material and placing the coated metal framework or coping in a furnace heated to a temperature below the melting temperature of the high fusing temperature metal particles but high enough to cause partial melting of the low fusing temperature metal particles although not complete melting. Partial melting causes a phase change in the low temperature fusing metal particles to occur and provided the heat treatment time period is adequate the partially melted low fusing particles will fuse to one another, to the high fusing temperature particles and to the metal surface of the metal framework. If complete melting of the low fusing particles occur the retentive properties of the bonder is diminished. To form a strong bond the high fusing temperature particles, low fusing temperature particles and the metal surface should be essentially oxide free. A flux in the bonder will maintain an oxide free surface.